This application is based on Patent Application No. 2001-126395 filed Apr. 24, 2001 in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a printing apparatus which has means for feeding a printing medium relative to a printing head having an array of printing elements, during a printing operation.
2. Description of the Related Art
In a printing apparatus of this kind, for example, a so-called serial printing apparatus which carries the printing head relative to a printing medium in a direction different from that of the array of the printing elements (main scan operation) and also feeds between the main scan operations the printing medium relative to the printing head in a direction perpendicular to the main scan direction (sub-scan operation) to perform printing of an image, there may be a case where a feeding amount of the printing medium between the main scan operations is set smaller than a printing element pitch in the printing head to realize a higher resolution than the printing element pitch. Setting the feeding amount to a smaller value, however, makes an overall feeding speed that much slower, resulting in a lowered throughput of the printing apparatus. Hence, it is a conventional practice to set the feeding amount as a sum of an amount of arranging width of a predetermined number of printing elements, which are arranged at a predetermined pitch, and an amount shorter than the printing element pitch, prepare a plurality of different feeding amounts, and combine these different feeding amounts as required, thereby striking a balance between a high resolution and a throughput.
For the printing operation, print data representing an image to be printed is mapped in print buffers associated with print dot forming positions in the main scan and sub-scan directions and, as the printing operation proceeds, the print data is transferred to the printing elements.
In a printing apparatus of a construction described above that realizes a higher resolution than the printing element pitch, two buffers are provided, one for mapping data that conforms the original printing element pitch and one for mapping interpolated data corresponding to a feeding amount smaller than the printing element pitch. Suppose the original printing element pitch in the printing head is 360 dpi (dots per inch). When the printing elements are located at the positions on the printing medium that match 360 dpi, the printing operation is done based on the data mapped in the print buffer for 360 dpi. When the printing elements are not located at the positions on the printing medium that match 360 dpi as a result of, for example, adjustments made on the feeding amount, the printing is performed based on data of the other print buffer in which the data is arranged to interpolate the 360-dpi print positions. With this control, if the feeding amount is set by adding {fraction (1/720)} inch to an integer multiple of {fraction (1/360)} inch, 720-dpi printing can be realized even when a printing head has a printing element pitch of 360 dpi.
The conventional printing apparatus described above, however, has the following problems.
1. Since the feeding amount of a printing medium does not necessarily match bytes, basic units used in data processing by computers, it is necessary to reconstruct the print buffers according to a particular feeding amount.
2. Control is complicated, so the software development takes long.
3. Since the print buffer is reconstructed, the processing time and the required capacity of a temporary storage area such as RAM increase.
The present invention is intended to solve these problems.
In an aspect of the present invention, there is provided a printing apparatus for performing a printing operation by using a printing head having an array of a plurality of printing elements, the printing apparatus comprising:
means for feeding a printing medium relative to the printing head;
feed control means for driving the feeding means to feed the printing medium and for controlling the feeding means to change a feeding amount of the printing medium;
means for transferring print data to the plurality of printing elements to cause the printing head to perform the printing operation; and
transfer control means for changing, according to the feeding amount, the number of clocks for transferring the print data.
The printing apparatus may comprise means for scanning the printing head relative to the printing medium in a direction different from that of the array of the printing elements, and wherein the feeding means may feed the printing medium in a direction perpendicular to the scanning direction.
The feed control means may change the feeding amount according to a resolution of printing.
The feed control means enables to set a driving amount of the feeding means to match a feeding amount less than a pitch of the printing elements in the printing head added to an integer multiple of the printing element pitch. Here, a plurality of kinds of the driving amount are provided. Further, the feed control means may be capable of combining a plurality of kinds of the driving amount.
In the above aspect of the present invention, when shifting the positions of data to be set in the plurality of printing elements by an amount less than a predetermined value in response to the changing of the feeding amount, the transfer control means may add a predetermined amount of blank data to the print data to be transferred and may reduce the number of clocks by an amount corresponding to the data position shifting. Here, the predetermined value may be 8 bits, a unit used for data processing.
In the above aspect of the present invention, the printing head may be in the form of an ink jet printing head for performing printing by ejecting an ink. Here, the ink jet printing head may have heating elements for generating thermal energy to make the ink to film-boil, as an energy for ejecting the ink.
Incidentally, in the present specification, xe2x80x9cprintingxe2x80x9d means not only a condition of forming significant information such as characters and drawings, but also a condition of forming images, designs, patterns and the like on printing medium broadly or a condition of processing the printing media, regardless of significance or lack of meaning or of being actualized in such manner as to be visually perceived by a human.
Further, the xe2x80x9cprinting mediumxe2x80x9d means not only a paper used in a conventional printing apparatus but also everything capable of accepting inks, such as fabrics, plastic films, metal plates, glasses, ceramics, wood and leathers, and in the following, will be also represented by xe2x80x9cpaperxe2x80x9d.
Further, the term xe2x80x9cinkxe2x80x9d should be interpreted in a broad sense like the definition of xe2x80x9cprintingxe2x80x9d above and thus the ink, by being applied on the printing media, shall mean a liquid to be used for forming images, designs, patterns and the like, processing the printing medium or processing inks.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.